This invention relates generally to liquid particle/droplet detecting systems, and more particularly to systems for detecting particles or droplets of liquids, e.g., oils, in gas systems making use of at least one gas compressor or other device which may introduce fine particles of such liquid(s) into gas in the system.
As should be appreciated by those skilled in the art, in gas producing, transport and/or storage systems, such as natural gas feed stock systems, fine oil mist may enter into the conduit carrying the natural gas as a result of leakage of oil from seals of compressors. The presence of such minute particles or droplets of oil (sometimes referred to as “oil droplet breakthrough”) can contaminate the natural gas. Moreover, oil mist in natural gas feed stock may reduce the efficiency of the hydrogenation catalyst by deactivating it and also causing it to “cake”, thereby creating a pressure drop across a hydrogenator/desulfurizer. Thus, it is a common practice to make use of separators, coalescers, adsorbent beds, and filters in gas systems downstream of the high pressure gas compressor (or any other device which may introduce fine oil particles into the gas). Such devices are designed to capture such oil particles and thereby prevent them from contaminating the final gas product. It has also been determined that in aircraft HVAC systems a mist of fine oil particles from some component in the air flow path may find its way into the ventilation system of the pilot's compartment and/or the passenger cabin. Obviously, this occurrence is undesirable.
The patented prior art includes various particle detecting devices that make use of light scattering techniques to detect the presence of particles in fluid streams. For example, in U.S. Pat. Nos. 5,864,399 (Girvin et al.) and 5,642,193 (Girvin et al.) there are disclosed particle detectors, each of which employs a laser disposed in a resonant cavity and an intra-cavity view volume. The resonant cavity is defined by two spaced apart mirrors, with the laser medium positioned between them, defining a light path. A pump source is optically coupled to drive the laser medium to produce coherent light having a first wavelength. The view volume is positioned in the light path, between the first mirror and the laser medium, to introduce particles into the resonant cavity so that light impinging there-upon produces scattered light. A detector is disposed to sense light scattered from the view volume and produces signals proportional to the light sensed. A displaying device, such as a pulse height analyzer, is in electrical communication to receive the signals produced by the detector to quantitatively display the intensity of the light sensed.
DE 10162278 discloses a system of detecting the presence of air compressor produced oil droplets in compressed gas stream by heating and expanding a partial aerosol stream, to thereby transform the droplets into a gas which is subsequently analyzed by a gas sensor.
Devices for detecting particles in a fluid stream are also commercially available. For example, Thermo Andersen, Inc., of Franklin, Mass. sells a HPM-1000 particulate monitor that is designed to be installed directly in line with compressed air/gas streams to provide continuous measurement of oil mist carryover, entrained water mist, and particulate contamination at pressures up to 350 psig. The HPM-1000 monitor uses a high sensitivity nephalometric (photometric) sensor, whose light scattering detection configuration has been optimized for the measurement of fine particle contamination in compressed air and gas streams.
While the aforementioned prior art is generally suitable for its intended purposes, it nevertheless leaves something to be desired from the standpoint of providing a monitoring system and method capable of detecting low levels of fine oil or other liquid particles in a gas stream from any device which may introduce fine oil or other liquid particles into the stream and to alert an operator to that fact. In our patent application Ser. No. 11/249,206 filed on Oct. 13, 2005, now U.S. Pat. No. 7,343,781, from which this application claims priority and which is assigned to the same assignee as this invention there is disclosed and claimed a system that addresses that need to provide an alert signal indicative of the presence of oil or other liquid particles in the gas. The alert signal can be used to institute automatic remedial action, e.g., shut off at least a part of the system and/or bring another part of the system on-line to prevent the further contamination of the gas product.
In particular, our U.S. Pat. No. 7,343,781 discloses a system for detecting fine liquid, e.g., oil, particles in a gas system having a high pressure compressor and at least two gas handling devices, e.g., a coalescer and at least one adsorber. The detection system uses plural sensors and a monitor unit. Each of the monitors is arranged for detecting the presence of fine liquid particles in the gas by means of light scattering and for providing an output signal to a data acquisition unit. The data acquisition unit operates in response to the detection of the fine liquid particles in various portions of the gas system and to provide alert signals in response thereto. The alert signals can be used to control associated valves in the gas system to bring about a desired result.
For some gas carrying systems, e.g., natural gas reformation system, HVAC systems such as in aircraft, clean rooms or other controlled environments in manufacturing facilities etc., the prior art systems as disclosed above may not be suitable, e.g., they may be too complex or expensive. Moreover, in some gas supply systems automated control may not be necessary. The systems and methods of the invention of our U.S. Pat. No. 7,343,781, absent its feed-back or automated control aspects, can be used for such simplified (e.g., non-automatic control) applications. Thus, the subject invention is directed to providing systems and methods to aid in identification of fine oil (or other liquid) particles into a downstream gas supply by monitoring the gas at one point and reacting to any appreciable increase in oil levels to provide a signal indicative of the absolute value of the liquid detected. Moreover, the systems and methods of the subject invention are capable of detecting extremely low levels of liquid particles. Thus, the usage of the systems and methods of this invention enables an early warning of oil/liquid droplet presence that may be an unsafe or unhealthy environment, or indicative of a pump/compressor/fan failure.
The disclosure of the previously identified patents, patent applications and publications is hereby incorporated by reference.